The present invention relates to cermet inert anodes which are useful for the electrolytic production of metals such as aluminum. More particularly, the invention relates to cermet inert anode materials and spray drying methods for making cermet inert anode materials.
The energy and cost efficiency of aluminum smelting can be significantly reduced with the use of inert, non-consumable and dimensionally stable anodes. Replacement of traditional carbon anodes with inert anodes allows a highly productive cell design to be utilized, thereby reducing capital costs. Significant environmental benefits are also possible because inert anodes produce essentially no CO2 or CF4 emissions. Some examples of inert anode compositions are provided in U.S. Pat. Nos. 4,374,050, 4,374,761, 4,399,008, 4,455,211, 4,582,585, 4,584,172, 4,620,905, 5,279,715, 5,794,112, 5,865,980 and 6,126,799, assigned to the assignee of the present application. These patents are incorporated herein by reference.
A significant challenge to the commercialization of inert anode technology is the anode material. Researchers have been searching for suitable inert anode materials since the early years of the Hall-Heroult process. The anode material must satisfy a number of very difficult conditions. For example, the material must not react with or dissolve to any significant extent in the cryolite electrolyte. It must not react with oxygen or corrode in an oxygen-containing atmosphere. It should be thermally stable at temperatures of about 1,000xc2x0 C. It must be relatively inexpensive and should have good mechanical strength. It must have high electrical conductivity at the smelting cell operating temperatures, e.g., about 900xc2x0 to 1,000xc2x0 C., so that the voltage drop at the anode is low.
In addition to the above-noted criteria, aluminum produced with the inert anodes should not be contaminated with constituents of the anode material to any appreciable extent. Although the use of inert anodes in aluminum electrolytic reduction cells has been proposed in the past, the use of such inert anodes has not been put into commercial practice. One reason for this lack of implementation has been the long-standing inability to produce aluminum of commercial grade purity with inert anodes. For example, impurity levels of Fe, Cu and/or Ni have been found to be unacceptably high in aluminum produced with known inert anode materials.
The present invention has been developed in view of the foregoing, and to address other deficiencies of the prior art.
The present invention relates to cermet inert anode materials which exhibit improved properties such as reduced porosity and the ability to produce commercial purity aluminum when used in an electrolytic aluminum production cell. The inert anode compositions, which are made by a spray drying process, comprise a ceramic phase and a metal phase. The ceramic phase preferably comprises oxides of nickel, iron and at least one other metal selected from Zn, Co, Al, Li, Cu, Ti, V, Cr, Zr, Nb, Ta, W, Mo, Hf and rare earths. The metal phase preferably comprises at least one metal selected from Cu, Ag, Pd, Pt, Au, Rh, Ru, Ir and Os. A preferred metal phase includes Cu and/or Ag, and may also include at least one noble metal selected from Pd, Pt, Au, Rh, Ru, Ir and Os.
An aspect of the present invention is to provide a method of making a cermet inert anode composition. The method includes the steps of providing a slurry comprising ceramic phase particles and metal phase particles, spray drying the slurry to form agglomerated particles comprising the ceramic phase and metal phase particles, and consolidating the spray dried particles to form the cermet inert anode composition comprising the ceramic phase and the metal phase. The ceramic phase may comprise an oxide of Ni, Fe and at least on additional metal selected from Zn, Co, Al, Li, Cu, Ti, V, Cr, Zr, Nb, Ta, W, Mo, Hf and rare earths. The metal phase preferably comprises at least one metal selected from Cu, Ag, Pd, Pt, Au, Rh, Ru, Ir and Os and may be in the form of a substantially pure metal, an alloy of the metal and/or a compound comprising the metal, e.g., CuO, Cu2O, Ag2O, etc.
Another aspect of the present invention is to provide a cermet inert anode composition comprising consolidated spray dried particles including ceramic and metal phases.
A further aspect of the present invention is to provide a method of making a composite powder. The method includes the steps of providing a slurry comprising ceramic phase particles and metal phase particles, and spray drying the slurry to form a powder including agglomerated particles comprising the ceramic phase and metal phase particles. The ceramic phase comprises an oxide of Ni and/or Fe, e.g., an oxide of Ni, Fe and at least one additional metal selected from Zn, Co, Al, Li, Cu, Ti, V, Cr, Zr, Nb, Ta, W, Mo, Hf and rare earths. The metal phase may comprise at least one metal selected from Cu, Ag, Pd, Pt, Au, Rh, Ru, Ir and Os.
Another aspect of the present invention is to provide a composite powder comprising spray dried particles including ceramic phase and metal phase particles.
A further aspect of the present invention is to provide a method of making a green compact of ceramic and metal phase particles. The method includes the steps of providing a slurry comprising ceramic phase particles and metal phase particles, wherein the ceramic phase comprises an oxide of Ni and/or Fe, spray drying the slurry to form agglomerated particles comprising the ceramic phase and metal phase particles, and pressing the spray dried particles to form the green compact.
Another aspect of the present invention is to provide a green compact of ceramic phase and metal phase particles comprising pressed spray dried particles including the ceramic phase and metal phase particles.
Other aspects and advantages of the invention will occur to persons skilled in the art from the following detailed description.